This invention relates to cadmium-free green emitting cathodoluminescent phosphors, and more particularly relates to ZnS : Cu, Al phosphors having higher color purity than prior green emitting ZnS-based and ZnCdS-based phosphors, and to a method for producing them and devices including them.
A standard green phosphor used widely in the production of cathode ray tubes for color television is a ZnCdS coactivated with Cu and Al. While the presence of cadmium in these phosphors is known to have certain beneficial effects, for example, the amount of cadmium may be adjusted to vary x and y coordinate values within a permissible range, nevertheless its cost and certain handling precautions could lead eventually to the use of cadmium-free cathode ray tube phosphors. Furthermore, phosphors containing cadmium tend to exhibit yellow body color and shifts in body color during processing, so called "bake-shifts".
While ZnS : Cu, Al phosphors having green cathodoluminescent emissions have been known for some time, (see for example U.S. Pat. No. 2,623,858 to Kroger on Dec. 30, 1952), such phosphors are characterized by low brightness levels and by the presence of significant blue emissions, resulting in low purity of the green emissions. Such characteristics render these phosphors unsuitable for use in conventional tri-dot color cathode ray tubes.